3 results on '"Duval, Florent"'
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2. ON THE (NON-)ENHANCEMENT OF THE Lyα EQUIVALENT WIDTH BY A MULTIPHASE INTERSTELLAR MEDIUM.
- Author
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LAURSEN, PETER, DUVAL, FLORENT, and STLIN, GÖRAN Ö
- Subjects
- *
INTERSTELLAR medium , *RADIATIVE transfer , *STARBURSTS , *PHOTON scattering , *ACCRETION (Astrophysics) , *ANISOTROPY - Abstract
It has been suggested that radiative transfer effects may explain the unusually high equivalent widths (EWs) of the Lyα line, observed occasionally from starburst galaxies, especially at high redshifts. If the dust is locked up inside high-density clouds dispersed in an empty intercloud medium, the Lyα photons could scatter off of the surfaces of the clouds, effectively having their journey confined to the dustless medium. The continuum radiation, on the other hand, does not scatter, and would thus be subject to absorption inside the clouds. This scenario is routinely invoked when Lyα EWs higher than what is expected theoretically are observed, although the ideal conditions under which the results are derived usually are not considered. Here we systematically examine the relevant physical parameters in this idealized framework, testing whether any astrophysically realistic scenarios may lead to such an effect. It is found that although clumpiness indeed facilitates the escape of Lyα, it is highly unlikely that any real interstellar media should result in a preferential escape of Lyα over continuum radiation. Other possible causes are discussed, and it is concluded that the observed high EWs are more likely to be caused by cooling radiation from cold accretion and/or anisotropic escape of the Lyα radiation. [ABSTRACT FROM AUTHOR]
- Published
- 2013
- Full Text
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3. THE Lyα REFERENCE SAMPLE. I. SURVEY OUTLINE AND FIRST RESULTS FOR MARKARIAN 259.
- Author
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Östlin, Göran, Hayes, Matthew, Duval, Florent, Sandberg, Andreas, Rivera-Thorsen, Thøger, Marquart, Thomas, Orlitová, Ivana, Adamo, Angela, Melinder, Jens, Guaita, Lucia, Atek, Hakim, Cannon, John M., Gruyters, Pieter, Herenz, Edmund Christian, Kunth, Daniel, Laursen, Peter, Mas-Hesse, J. Miguel, Micheva, Genoveva, Otí-Floranes, Héctor, and Pardy, Stephen A.
- Subjects
METAPHYSICAL cosmology ,GALAXIES ,STARBURSTS ,RADIATIVE transfer ,ELECTROMAGNETIC wave propagation - Abstract
The Lyα Reference Sample (LARS) is a substantial program with the Hubble Space Telescope (HST) that provides a sample of local universe laboratory galaxies in which to study the detailed astrophysics of the visibility and strength of the Lyαline of neutral hydrogen. Lyα is the dominant spectral line in use for characterizing high-redshift (z) galaxies. This paper presents an overview of the survey, its selection function, and HST imaging observations. The sample was selected from the combined GALEX+Sloan Digital Sky Survey catalog at z = 0.028-0.19, in order to allow Lyα to be captured with combinations of long-pass filters in the Solar Blind Channel (SBC) of the Advanced Camera for Surveys (ACS) onboard HST. In addition, LARS utilizes Hα and Hβ narrowband and u, b, i broadband imaging with ACS and the Wide Field Camera 3 (WFC3). In order to study galaxies in which large numbers of Lyα photons are produced (whether or not they escape), we demanded an Hα equivalent width W(Hα) ⩾100 Å. The final sample of 14 galaxies covers far-UV (FUV, λ ∼ 1500 Å) luminosities that overlap with those of high-z Lyα emitters (LAEs) and Lyman break galaxies (LBGs), making LARS a valid comparison sample. We present the reduction steps used to obtain the Lyα images, including our LARS eXtraction software (LaXs), which utilizes pixel-by-pixel spectral synthesis fitting of the energy distribution to determine and subtract the continuum at Lyα. We demonstrate that the use of SBC long-pass-filter combinations increase the signal-to-noise ratio by an order of magnitude compared to the nominal Lyα filter available in SBC. To exemplify the science potential of LARS, we also present some first results for a single galaxy, Mrk 259 (LARS #1). This irregular galaxy shows bright and extended (indicative of resonance scattering) but strongly asymmetric Lyα emission. Spectroscopy from the Cosmic Origins Spectrograph on board HST centered on the brightest UV knot shows a moderate outflow in the neutral interstellar medium (probed by low ionization stage absorption features) and Lyα emission with an asymmetric profile. Radiative transfer modeling is able to reproduce the essential features of the Lyα line profile and confirms the presence of an outflow. From the integrated photometry we measure an Lyα luminosity of L
Lyα =1.3 × 1042 erg s–1 an equivalent width W(Lyα) = 45 Å and an FUV absolute magnitude MFUV = –19.2 (AB). Mrk 259 would hence be detectable in high-z Lyα and LBG surveys. The total Lyα escape fraction is 12%. This number is higher than the low-z average, but similar to that at z > 4, demonstrating that LARS provides a valid comparison sample for high-z galaxy studies. [ABSTRACT FROM AUTHOR]- Published
- 2014
- Full Text
- View/download PDF
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